1. Field of the Invention
This invention relates to a process for producing an organosilicon resin, and a process for producing a polyurethane foam by using the organosilicon resin obtained by that process. More particularly, this invention relates to a process for producing a polyurethane foam superior in properties such as dimensional stability because of an improvement in storage stability of a resin premix.
2. Description of the Prior Art
Polyurethane foams are commonly produced by blowing and curing a polyurethane foam composition containing a polyol, a polyisocyanate, water or carbon dioxide as a blowing agent, and an amine as a catalyst. Before use or during storage, this composition is usually divided into the polyisocyanate and a resin premix prepared by mixing the polyol, the blowing agent, the catalyst and a foam stabilizer. In such a production process, for the purpose of improving the appearance and other physical properties of the resulting foams, it is proposed to add to the resin premix an additive which is incompatible with it. This additive is useful for improving dimensional stability of the resulting polyurethane foams especially in the case of compositions making use of water as the blowing agent. Proposed as the additive of this type are, for the production of semi-hard polyurethane foams, carbon black (Japanese Laying-open Patent Publication (Kokai) No. 55-135128); and, for the production of hard polyurethane foams, powdery or fibrous potassium titanate (Japanese Laying-open Patent Publication (Kokai) No. 56-14535) and an organosilicon compound having as structural units an R.sub.3 SiO.sub.1/2 unit (wherein R's are the same or different and each represent a monovalent hydrocarbon group having 1 to 6 carbon atoms) and an SiO.sub.2 unit (Japanese Laying-open Patent Publication (Kokai) No. 5-19469/ or its corresponding U.S. Pat. No. 2,722,952).
These additives, however, are not compatible with the resin premix, and hence have had problems that they separate from the resin premix or deteriorate because of an alkali catalyst in the resin premix, making it impossible to exhibit the intended properties of improving dimensional stability. Accordingly, it has conventionally been necessary to agitate the resin premix so as to be uniformly mixed and dispersed, before its use, i.e., before it is mixed with the polyisocyanate to cause reaction (foaming and curing), bringing about another problem that foaming means are restricted, e.g., the resin premix can not be used in spray foaming. In order to solve these problems, it has been sought to develop an additive which is compatible with the resin premix and therefore well dispersible in the resin premix and is highly hydrophobic and low reactive.